1. The Field of the Invention
The present invention relates to detecting malfunctions in electronic circuitry. More particularly, embodiments of the invention relate to detecting electrical overstress events in electronic circuitry such as optical emitters.
2. Related Technology
Electronic circuitry is increasingly integrated into data communication and data processing devices. For example, integrated circuits, often referred to as a microchips or simply chips, are used in a variety of applications, such as high speed optical networks. One type of chip, the laser diode chip, plays an increasingly important role in modern high speed optical networks. Laser diode chips are complex semiconductor devices that convert an electrical data signal into an optical data signal. A laser diode chip, also known simply as a laser, is an essential component of a transmitter optical sub assembly (TOSA). A TOSA is often paired with a receiver optical sub assembly (ROSA) in an optoelectronic transceiver.
Examples of lasers that can be integrated into optoelectronic transceivers include vertical cavity surface emitting lasers (VCSELs) and edge emitting lasers. While VCSELs and edge emitting lasers exhibit desirable performance characteristics, they also have the unfortunate drawback of being very susceptible to electrical overstress (EOS) events. EOS events include events that can cause failure in a laser and are characterized by exposure of the laser to excessive voltage, current, and/or power. An electrostatic discharge (ESD) event is a particular type of EOS event where a rapid transfer of electrostatic charge occurs between two objects. EOS events, and ESD events in particular, can damage a laser in many ways, often resulting in observable signs of damage or failure attributes.
EOS damage is not always obvious though. In fact, some EOS events damage a laser without leaving any apparent visible manifestation of the damage. Such EOS events can still render the laser non-functional, even if no physical anomalies are visibly evident. Less damaging EOS events may also occur. Although these less damaging EOS events may not render the laser non-functional, these EOS events can shift the parametric performance of the laser, thus causing the laser to produce an inaccurate optical data signal.
Often when an optoelectronic transceiver containing a malfunctional laser is returned by a customer, it becomes necessary for the manufacturer to determine what caused the laser to malfunction. For example, it may be necessary for the manufacturer of a particular optoelectronic transceiver to make a determination as to whether the laser of the optoelectronic transceiver malfunctioned due to an ESD event, or whether the laser malfunctioned due to some other cause, such as a growth defect in the laser. Where there is no apparent visible manifestation of on a laser surface, the processes of performing a failure analysis on the laser can be very costly in terms of time and expense.
It would therefore be useful to be able to readily detect the occurrence of an EOS event which caused a particular laser to malfunction in order to save the time and expense of performing a failure analysis on the laser.